An amplifier assembly and operating method for an amplifier assembly are known, for example, from U.S. Pat. No. 6,133,788 A and from U.S. Pat. No. 6,285,251 B.
It is known that an individual amplifier attains its maximum efficiency only when it is operated at its maximum saturated output level (or at least close to the latter). In order to be able to maintain the maximum efficiency over a relatively large power range, therefore, amplifier assemblies having two amplifiers are used. The two amplifiers are operated in such a way that they both operate at their maximum saturated output level. The output signals are combined to form a useful signal by means of a suitable coupling element. The amplitude of the useful signal is set by the phase offset of the two output signals being correspondingly set. In general, a hybrid or a ring coupler is used as the coupling element.
If the phase offset of the output signals differs from zero, a loss signal also arises in addition to the useful signal. The loss signal leads to negative reactions affecting the amplifiers. In order to avoid such reactions, it is possible to provide a resistor, for example, which converts the loss signal into heat. The use of the resistor improves the operating conditions (reduced reactions affecting the amplifiers, reduced distortions, etc.) of the amplifier assembly. However, the resistor leads at the same time—particularly in the case of a large phase offset, i.e. a small partial power of the useful signal—to a reduced total efficiency of the amplifier assembly.
The amplifier assemblies mentioned are used, inter alia, in mobile radio devices. They are also used in other battery-powered devices. The energy efficiency is of particular importance in battery-powered devices. Therefore, attempts have already been made to use, instead of the resistor, a rectifier device which rectifies the loss signal and feeds the rectified loss signal to a power supply device of the amplifier assembly.
In conventional systems, the rectifier device is constructed using uncontrolled rectifier elements (=diodes). When such rectifier elements are used, the limiter effect of the rectifier elements cannot be influenced. As a result, the effective resistance of the rectifier device is modulation-dependent, i.e., dependent on the phase offset of the output signals from one another. On account of the variability of the effective resistance of the rectifier device, the rectifier device is not well matched for all phase offsets. For some phase offsets, reflections into the amplifiers occur, which, for their part, result in nonlinear distortions and reductions of efficiency.